This invention relates to an extruding die for producing ceramic honeycomb structural bodies, and more particularly to ceramic batch supply apertures of an extruding die for extruding ceramic honeycomb structural bodies.
Ceramic honeycomb structural bodies are effective as catalyst carriers for purifying exhaust gases of internal combustion engines, or are effective as filters for filtering fine particles and the like. These honeycomb structural bodies are usually made of a ceramic material such as cordierite, alumina, silicon carbide and the like, and owing to their configurations, they are generally produced by an extruding method.
An extruding die for use in the extruding method has been known and is disclosed in U.S. Pat. No. 3,905,743, wherein the die is formed on one side with ceramic batch supply apertures 41 for supplying a ceramic batch by means of an extruding molding machine and on the other side with ceramic batch exhaust grooves 42 corresponding in sectional shape to a ceramic honeycomb structure body to be extruded, as shown in FIG. 1. Another extruding die has been known and is disclosed in Japanese Laid-open Patent Application No. 58-217,308, wherein ceramic batch reservoirs 43 are provided between ceramic batch supply apertures 41 and ceramic batch exhaust grooves 42 as shown in a partial perspective view of FIG. 2.
In order to particularly define or control the flow of ceramic batch to obtain perfect ceramic honeycomb structural bodies, it has been proposed to provide a perforated plate (Japanese Patent Application Publication No. 53,844/84) or a flow rectifier plate (Japanese Patent Application Publication No. 46,763/84) on a ceramic batch supplying side of a die.
These ceramic batch supply apertures in extruding dies are formed by drilling holes with drills made of hard metals such as die steels. When the supply apertures are considerably long in comparison with diameters thereof, dimensional accuracy of the supply apertures on a side of the exhaust grooves becomes lower. Moreover, irregularities in roughness of inner surfaces of the supply apertures become large because of the multiplicity of the apertures. As a result, flow of the ceramic batch passing through the supply apertures becomes uneven, so that perfect ceramic honeycomb structural bodies cannot be produced. This is particularly acute in ceramic batch supply apertures having very small diameters which would obtain honeycomb structure bodies having cells with a high density.
In order to solve these problems, ceramic batch supply apertures have been finished by honing in manufacturing extruding dies to improve the surface roughness. As an alternative, a die is separated into two parts which are jointed together after working. These methods are not acceptable from an economical viewpoint.
The methods of particularly defining the flow of ceramic batch using the perforated plate or flow rectifier plate as above described, permit the control of the flow just before the ceramic batch supply apertures, but do not define the flow by the supply apertures, themselves. Accordingly, such methods are insufficient to directly adjust irregularities in individual resistance of the flow in the supply and exhaust apertures. In extruding honeycomb structural bodies having cells distributed with different densities, therefore, these methods of the prior art encounter great difficulties.